In conventional cathode ray tube deflection processing, analog signals are used to control the current provided to a deflection coil and to control the voltage applied to a focus grid. However, the analog technique is limited by a distortion phenomenon generated in an irregular shape due to flattening of the screen of the cathode ray tube (CRT) and generated by a deflection yoke coil. Control of such phenomena is complicated and difficult to fine tune. A plurality of control terminals are required in order to elaborately and minutely correct the distortion phenomenon. In addition, a well-known phenomenon referred to as north-south (NS) pincushion distortion is uncorrectable, and an additional tilt correcting coil is required for correcting tilt.
Furthermore, in conventional analog deflection devices, electric high tension (EHT) is evenly maintained regardless of the amount of beam in order to correct distortion due to the EHT fluctuation, resulting in increased manufacturing expenses.
In computer CRT applications, the frequencies of horizontal and vertical synchronous signals provided to the cathode ray tube can vary over a wide range. For example, the frequency of the horizontal synchronous signal input to the deflection processing device can vary from 15 kHz to 120 kHz, according to the video output mode of the computer, for example VGA mode or SGA mode. Processing of signals over such a wide range is hardware intensive. Moreover, when the frequencies of horizontal synchronous signals vary over a wide range, a Moire phenomenon is produced, in which the colors of the displayed screen spread like a wave.